Gear finishing



Feb. 16, 1943. R. s. DRUMMOND GEAR FINISHING 7 Fil ed Jan. 22, 1940 FIGQI.

FIG.2.

- FIG.4.

FIG.5.

INVEN TOR.

ROB

m WW N O m n M m D-I s R E Patented Feb. 16, 1943 UNITED STATES PATENT OFFICE GEAR FINISHING Robert S. Drummond, Detroit, Mich.

Application January 22, 1940, Serial No. 315,106

9 Claims.

The present invention relates to gear finishing and more particularly to a new method of longitudinally crowning teeth of gears. There has recently been considerable interest shown in crowned gears for the reason that these gears ofier important advantages over uncrowned gears. They operate more silently under ordinary conditions, and in addition a pair of crowned gears running in mesh may operate satisfactorily without end interference even though there is slight misalignment of the shafts.

According to the present invention, I propose to crown the teeth of a work gear longitudinally, or from end to end, by rotating the gear in mesh with a gear-like finishing tool, with the axes of the gear and finishing tool crossed, and by providing a relative oscillation between the gear and tool about an axis which is parallel to the common normal to the axes of both the gear and tool. The crowning may be accomplished by this oscillation alone, or in some cases it may be combined with a relative translation in a plane parallel to the axes of both the gear and tool.

It is accordingly an object of the present invention to finish gear teeth in a manner to crown said teeth longitudinally by rotating the gear in mesh with the gear-like finishing tool at crossed axes and by imparting a relative oscillation to the gear and tool" about an axis which is parallel to the common normal to the axes of said gear and tool.

It is a further object of the present invention to prac ice the foregoing method with a finishing tool having two axially spaced gear-like members so that the mid portion of the teeth of the work gear will not be contacted.

It is a further object of the present invention to practice the foregoing method with the gear and gear-like finishing tool in loose mesh so that no finishing action will take place adjacent the center of the gear teeth.

Other objects of the invention will be apparent as the description proceeds, and when taken in conjunction with the accompanying drawing wherein:

In Figure 1 I'have illustrated diagrammatically the relationship between the gear and cutter;

Figure 2 is a diagrammatic View looking downward in Figure 1;

Figure 3 is a diagrammatic view illustrating a modified type of cutter;

Figure 4 is a diagrammatic view looking downward in Figure 3; and

Figure 5 is a side elevation partly in section of the composite cutting tool illustrated in Figures 3 and 4.

The present invention relates generally to the same type of gear finishing as disclosed in my prior Patent 2,157,981. In this type of gear finishing the tool is preferably a cutting tool in the form of a gear conjugate to the gear to be finished. The tool is made of high-speed steel, and the teeth are provided with serrations extend ing generally up and down the faces of the teeth.

When placed in mesh with the work gear with the axles of the gear and tool crossed at a limited angle, limited contact is had between the teeth of the gear and tool. Rotation of the gearand tool in mesh generates a narrow band extending generally up and down the face of the gear teeth, and this is normally spread from end to end of the gear teeth by providing a relative translation between the gear and the cutter.

In my prior patent I have disclosed the crowning of the teeth by superimposing a timed oscillation upon this translation in a manner to remove more metal from the ends of the gear teeth than from the middle thereof. In the prior patent this relative oscillation takes place about an axis perpendicular to the axis of the work gear, and adapted generally to move the ends of the gear teeth inwardly with respect to the tooth spaces on the cutter.

According to the present invention the relative oscillation between the gear and tool takes place about an axis parallel to the common normal to the axes of the gear and tool. Ordinarily this oscillation takes place about the common normal to these axes. This oscillation may be practiced without translation, or it may be combined with translation in a definite manner to produce different desired results.

It will be apparent that the result accomplished by the present method is substantially different from that in my prior patent. 'Inthe present case, instead of moving the ends of the gear teeth relatively inward with respect to the cutter, the ends of the gear teeth ,are moved laterally with respect thereto. This results in finishing the ends of the gear teeth at a different helix angle, and'further results in a relative feed effect between the teeth longitudinally thereof.

Referring first to Figures 1 and 2, I have illustrated diagrammatically a gear G and a cutter C. I have illustrated the cutter C as somewhat wider than the gear G, a condition which is necessary in the present method. The teeth of the cutter C and gear G are conjugate, but extend at difierent helix angles, with the result that the gear and cutter are in tight mesh when their axes extend obliquely to each other, or are crossed in space.

In Figure 2 the arrow 10 indicates the direction of relative oscillation, and I have indicated at II the center of crossed axes," which, as will be recognized, is determined by the common normal to the axes of the gear (3 and the cutter C. It will be readily evident that this oscillation will be accomplished by oscillating either the cutter C or gear G about the axis I I, or it may be accomplished by simultaneously oscillating both members.

when the gear G and cutter C are brought into tight mesh with their axes crossed, as indicated in Figure 2, so that the center of the gear teeth contact the center of the cutter teeth, rotation of the two parts will generate a band extending generally up and down the gear teeth and substantially at the center thereof. This is for the reason that the two surfaces of the gear and cutter are convex surfaces which theoretically contact each other only at a point. Relative oscillation in the direction of the arrow l shifts the point of contact longitudinally of the teeth and, as will be evident, eventually produces marked end contact on the narrower member, which is illustrated herein as being a gear. During this relativeoscillation, however, the point of contact shifts gradually longitudinally of the gear teeth in a manner which constitutes a feeding eflect. Thus without providing any translation the teeth of the gear are finished from end to end, and are in addition lon itudinally crowned from end to end so that said teeth are thicker in the middle portion than at the ends. Therelative oscillation is relatively slow so as to provide the gradually shifting point of contact referred to above. To produce symmetrically crowned teeth, the relative oscillation is of course carried to equal amounts from the initial position of tight mesh.

While this method of gear crowning gives satisfactory results, it is in some cases desirable to combine the oscillation referred to with the relative translation, such for example as in the direction of the arrow i2 in Figure 2. This translation is in a plane parallel to the axes of both the gear and the cutter and would of itself tend to result in uniformly finished gear teeth. When combined with the oscillation, however, it serves to modify the crowning effect resulting from the oscillation.

As will be evident, the motions referred to may be accomplished by any suitable mechanism, and in the event that combined oscillation and translation is desired, it is preferably accomplished by suitable mechanism which causes the oscillation to take place as a result of the translation. Thus for example, the arbor which supports either the gear or tool may be mounted for pivoting movement, and may have connected thereto a pin which moves in a stationary inclined slot. Means of this type for accomplishing a distinctly different crowning motion are illustrated in my prior patent.

As stated above, the finishing action which results from oscillation and/or translation result in gear teeth which are accurately finished from end to end as well as teeth which are longitudinally crowned. The shaving action which follows the practice of this method removes fine slivers of metal and finishes the gear teeth to within very narrow limits of accuracy.

of the gear teeth, the method practiced may be substantially the same, except that when the gear and cutter are placed in. initial mesh in mid portion they are left in loose mesh. As a result of this, the oscillation for a short distance either side of the center position does not force the cutter teeth into cutting relation with the gear teeth. Further oscillation results in removing metal from a point located between the center of the gear teeth to the ends of said teeth.'

Preferably this type of gear finishing is combined with the conventional shaving operation so as to accurately finish the mid portion of the teeth which are not affected by this type of crownlns operation.

In Figures 3 and 4 I have illustrated a similar method in which the gear G is operated on by a composite cutter C composed of two individual gear-like members I3 and It. The members II and H are axially spaced, and as will be evident from Figures 3 and 4, the members l8 and N are out of contact with the mid portion of the teeth of the gear (3-. Relative oscillation between these members is the same as illustrated in.

Figures 1 and 2; that is, in the direction of the arrow 20 in Figure 4, which is about an axis parallel to the common normal to the axes of said gear and cutter, and preferably about the common normal itself. As in the previous case, this oscillation may be practiced alone, or it may be comined with a timed relative translation.

In Figure 5 I have illustrated more or less diagrammatically a composite cutter C, such as illustrated in Figure 3, in which the members II and H are mounted on an arbor l5. In this tool it is necessary that the teeth of the members II and i4 shall be properly aligned, and for this purpose I provide a helical spline 16 on the arbor ii. The members I3 and I are provided with central openings having correspondingly inclined grooves for the reception of the splines. The arbor I5 is provided with an abutment II which may be integrally or otherwise secured thereto, and the members i3 and I4 are held against the abutment II by a suitable lock nut ill or the like. The spacing between the members It and I4 is provided by a spacer l9, and this spacer may be changed to provide different spacing. As is evident, due to the splined arrangement previously referred to, the teeth of the members I! and I will be properly aligned irrespective of their spacing.

The present specific disclosure is given to enable those skilled in the art to practice the present invention, the scope of which is illustrated by the appended claims.

What-I claim as my invention'is:

1. The method of crowning gears which comprises meshing a gear member to be crowned with a gear-like cutting member with their axes crossed at an angle less than 30' so that the common normal to their axes is centrally located with respect to said gear; rotating one of said If it is desired to modify only the end portions 15 members about its axis, thereby driving the other member, and relatively oscillating said members about said common normal to said axes.

2. The method of crowning gears which comprises providing a gear-like cutting member of such helix angle with respect to a gear member to be crowned that said members are adapted to mesh tightly with their axes crossed at an angle of less than 30, bringing said members into loose mesh so that the common normal to their axes is centrally located with respect to said gear, and

relatively oscillating said members about the common normal to their axes.

3. The method oi crowning a gear member which comprises meshing said gear member with a tool member comprising axially separated gearlike cutters so that said cutters contact said gear member only at points separated from the mid portion of the teeth of said gear member, and so that the common normal to their axes is centrally located with respect to said gear, and with the axes of said members crossed at an angle of less than 30, and relatively oscillating said members about the common normal to their axes.

4. The method of crowning gears which comprises meshing a gear member to be crowned with a gear-like cutting member with their axes crossed at an angle less than 30 so that the common normal to their axes is centrally located with respect to said gear, rotating one of said members about its axis, thereby driving the other member, relatively translating said members in a plane parallel to the axes of said members uniformly in opposite directions from the defined initial position, and simultaneously imposing a relative oscillation on said members about the common normal to their axes.

5. The method of crowning gears which comprises meshing a gear member to be crowned with a gear-like cutting member with their axes crossed at an angle less than 30 so that the common normal to their axes is centrally located with respect to said gear, rotating one of said members about its axis, thereby driving the other member, and relatively oscillating said members about an axis parallel to and substantially adjacent the common normal to the axes of said members.

6. The method of crowning gears which comprises meshing a gear member to be crowned with a gear-like cutting member with their axes crossed at an angle less than 30 so that the common normal to their axes is centrally located with respect to said gear, rotating one of said members about its axis, thereby driving the other member, relatively translating said members in a plane parallel to the axes of said members, and simultaneously imposing a relative oscillation about an axis parallel to and substantially adjacent the common normal to the axes of said members in timed relation to said translation.

7. The method of crowning a gear which comprises meshing a gear member to be crowned with a gear-like tool member wider than the gear member and wit-h their axes crossed at a limited angle less than 30", supporting one of said members for free rotation and driving said other member in rotation, thereby driving said one member, and imposing on the relative movement of said members in rotation a single additional relative crowning motion, said additional motion being a slow relative oscillation about the common normal to the axes of said members.

8. The method of crowning a gear which comprises meshing a gear member to be crowned with a gear-like tool member wider than the gear member and with their axes crossed at a limited angle less than 30 with the common normal to the axes of said members located midway between the end faces of the gear member, supporting one of said members for free rotation and driving said other member in rotation, thereby driving said one member, and imposing on the relative movement of said members in rotation a single additional relative crowning motion, said additional motion being a slow relative oscillation about the common normal to the axes of said members.

9. The method of crowning a gear which comprises meshing a gear member to be crowned with a gear-like tool member wider than the gear member and with their axes crossed at a limited angle less than 30 withthe common normal to the axes of 'said members located midway between the end faces of the gear member, sup-- 

